The diagnosis and treatment of many body ailments depends upon an accurate reading of the internal or core temperature of a patient's body temperature reading, and in some instances, upon comparison to a previous body temperature. For many years, the most common way of taking a patient's temperature involved utilization of Mercury thermometers. However, such thermometers are susceptible to breaking and must be inserted and maintained in the rectum or mouth for several minutes, often causing discomfort to the patient.
Because of the drawbacks of conventional Mercury thermometers, electronic thermometers were developed and are now in widespread use. Although electronic thermometers provide relatively more accurate temperature readings than Mercury thermometers, they nevertheless share many of the same drawbacks. For example, even though electronic thermometers provide faster readings, some time must still pass before an accurate reading can be taken. Moreover, electronic thermometers must still be inserted into the patient's mouth, rectum or axilla.
Tympanic thermometers, those thermometers that sense the infrared emissions from the tympanic membrane, provide nearly instantaneous readings of core temperature without the undue delay of other thermometers. The tympanic thermometer is generally considered by the medical community to be superior to oral, rectal, or axillary sites for taking a patient's temperature. This is because the tympanic membrane is more representative of the body's internal or core temperature and more responsive to changes in core temperature.
Conventional tympanic thermometers typically include two sensors. One sensor is a primary temperature sensor for measuring the temperature of the tympanic membrane. In one conventional tympanic thermometer, the primary temperature sensor is an infrared sensor, such as a thermopile. The thermopile is adapted to measure the emitted radiation of the tympanic membrane to determine the temperature of the membrane, without contacting the membrane. The other sensor is a reference temperature sensor for measuring the temperature of the primary temperature sensor, or thermopile. In one conventional tympanic thermometer, the reference temperature sensor is temperature-dependent resistor, such as a thermistor or a polysilicon resistor, mounted on the cold junction of the thermopile. Because the response of the thermopile is dependent upon the temperature of the thermopile itself, the ambient temperature of the resistor may be utilized to estimate the temperature of the thermopile to compensate for the thermopile's temperature dependency.
Typically, tympanic thermometers require calibration at the factory during manufacturing in order achieve the quick and accurate temperature reading capability noted above. Calibration of the tympanic thermometer at the factory requires individual calibration of each thermometer unit so that the proper calibration parameters of each individual thermometer can be written to the memory (e.g., EEPROM) of each thermometer's microprocessor. These calibration parameters involve determining the proper values for variables representing the sensors within each thermometer and any parameters related to the optical system, such as the geometry of the primary temperature sensor with respect to the ear canal and the device housing. Once these calibration parameters are determined and written to the memory of each thermometer, calibration is complete and the unit is shipped for sale. Unfortunately, known techniques for calibrating the tympanic thermometer fail to account for differences (e.g., manufacturing differences) in reference temperature sensors and assume that each of the reference temperature sensors responds in the same manner to a given input. Other known techniques may also rely upon the calibration of the primary temperature sensor to provide sufficiently accurate data to extract parameters of the reference temperature sensor. Aspects of the present invention involve a calibration process whereby both the reference temperature sensor and the primary temperature sensor are calibrated.
In addition, conventional methods for calibration often utilize a temperature-controlled water bath to control the temperature of the thermometer, or its components, during calibration. Because water is a conductor of electricity, the thermometer or its components are typically placed into a bag before immersion in the water bath. The bag acts as a barrier to block the water from contacting the thermometer or thermometer components while immersed in the bath. Utilizing such a bag creates various issues, including additional bag loading and bag unloading steps, potential bag leaks, condensation within the bag, an air gap between the bag and the thermometer or thermometer components, and increased calibration time due to temperature control of the bag and air gap. Aspects of the embodiments of the present invention invoke a process whereby the user of such bags is avoided.